Interaction of human NAD(P)H:quinone oxidoreductase 1 (NQO1) with the tumor suppressor protein p53 in cells and cell-free systems

Impact of NQO1 dysregulation in CNS disorders

NAD(P)H Quinone Dehydrogenase 1 (NQO1) plays a pivotal role in the regulation of neuronal function and synaptic plasticity, cellular adaptation to oxidative stress, neuroinflammatory and degenerative processes, and tumorigenesis in the central nervous system (CNS). Impairment of the NQO1 activity in the CNS can result in abnormal neurotransmitter release and clearance, increased oxidative stress, and aggravated cellular injury/death. Furthermore, it can cause disturbances in neural circuit function and synaptic neurotransmission. The abnormalities of NQO1 enzyme activity have been linked to the pathophysiological mechanisms of multiple neurological disorders, including Parkinson's disease, Alzheimer's disease, epilepsy, multiple sclerosis, cerebrovascular disease, traumatic brain injury, and brain malignancy. NQO1 contributes to various dimensions of tumorigenesis and treatment response in various brain tumors. The precise mechanisms through which abnormalities in NQO1 function contribute to these neurological disorders continue to be a subject of ongoing research. Building upon the existing knowledge, the present study reviews current investigations describing the role of NQO1 dysregulations in various neurological disorders. This study emphasizes the potential of NQO1 as a biomarker in diagnostic and prognostic approaches, as well as its suitability as a target for drug development strategies in neurological disorders.

Structural dynamics at the active site of the cancer-associated flavoenzyme NQO1 probed by chemical modification with PMSF

A large conformational heterogeneity of human NAD(P)H:quinone oxidoreductase 1 (NQO1), a flavoprotein associated with various human diseases, has been observed to occur in the catalytic site of the enzyme. Here, we report the X-ray structure of NQO1 with phenylmethylsulfonyl fluoride (PMSF) at 1.6 Å resolution. Activity assays confirmed that, despite being covalently bound to the Tyr128 residue at the catalytic site, PMSF did not abolish NQO1 activity. This may indicate that the PMSF molecule does not reduce the high flexibility of Tyr128, thus allowing NADH and DCPIP substrates to bind to the enzyme. Our results show that targeting Tyr128, a key residue in NQO1 function, with small covalently bound molecules could possibly not be a good drug discovery strategy to inhibit this enzyme.

Targeting HIF-1α Function in Cancer through the Chaperone Action of NQO1: Implications of Genetic Diversity of NQO1

HIF-1α is a master regulator of oxygen homeostasis involved in different stages of cancer development. Thus, HIF-1α inhibition represents an interesting target for anti-cancer therapy. It was recently shown that the HIF-1α interaction with NQO1 inhibits proteasomal degradation of the former, thus suggesting that targeting the stability and/or function of NQO1 could lead to the destabilization of HIF-1α as a therapeutic approach. Since the molecular interactions of NQO1 with HIF-1α are beginning to be unraveled, in this review we discuss: (1) Structure–function relationships of HIF-1α; (2) our current knowledge on the intracellular functions and stability of NQO1; (3) the pharmacological modulation of NQO1 by small ligands regarding function and stability; (4) the potential effects of genetic variability of NQO1 in HIF-1α levels and function; (5) the molecular determinants of NQO1 as a chaperone of many different proteins including cancer-associated factors such as HIF-1α, p53 and p73α. This knowledge is then further discussed in the context of potentially targeting the intracellular stability of HIF-1α by acting on its chaperone, NQO1. This could result in novel anti-cancer therapies, always considering that the substantial genetic variability in NQO1 would likely result in different phenotypic responses among individuals.

Effect of Kaempferol and Its Glycoside Derivatives on Antioxidant Status of HL-60 Cells Treated with Etoposide

Kaempferol is a well-known antioxidant found in many plants and plant-based foods. In plants, kaempferol is present mainly in the form of glycoside derivatives. In this work, we focused on determining the effect of kaempferol and its glycoside derivatives on the expression level of genes related to the reduction of oxidative stress—NFE2L2, NQO1, SOD1, SOD2, and HO-1; the enzymatic activity of superoxide dismutases; and the level of glutathione. We used HL-60 acute promyelocytic leukemia cells, which were incubated with the anticancer drug etoposide and kaempferol or one of its three glycoside derivatives isolated from the aerial parts of Lens culinaris Medik.—kaempferol 3-O-[(6-O-E-caffeoyl)-β-d-glucopyranosyl-(1→2)]-β-d-galactopyranoside-7-O-β-d-glucuropyranoside (P2), kaempferol 3-O-[(6-O-E-p-coumaroyl)-β-d-glucopyranosyl-(1→2)]-β-d-galactopyranoside-7-O-β-d-glucuropyranoside (P5), and kaempferol 3-O-[(6-O-E-feruloyl)-β-d-glucopyranosyl-(1→2)]-β-d-galactopyranoside-7-O-β-d-glucuropyranoside (P7). We showed that none of the tested compounds affected NFE2L2 gene expression. Co-incubation with etoposide (1 µM) and kaempferol (10 and 50 µg/mL) leads to an increase in the expression of the HO-1 (9.49 and 9.33-fold at 10 µg/mL and 50 µg/mL, respectively), SOD1 (1.68-fold at 10 µg/mL), SOD2 (1.72-fold at 10–50 µg/mL), and NQO1 (1.84-fold at 50 µg/mL) genes in comparison to cells treated only with etoposide. The effect of kaempferol derivatives on gene expression differs depending on the derivative. All tested polyphenols increased the SOD activity in cells co-incubated with etoposide. We observed that the co-incubation of HL-60 cells with etoposide and kaempferol or derivative P7 increases the level of total glutathione in these cells. Taken together, our observations suggest that the antioxidant activity of kaempferol is related to the activation of antioxidant genes and proteins. Moreover, we observed that glycoside derivatives can have a different effect on the antioxidant cellular systems than kaempferol.

Roles of NAD(P)H:quinone Oxidoreductase 1 in Diverse Diseases

NAD(P)H:quinone oxidoreductase (NQO) is an antioxidant flavoprotein that catalyzes the reduction of highly reactive quinone metabolites by employing NAD(P)H as an electron donor. There are two NQO enzymes—NQO1 and NQO2—in mammalian systems. In particular, NQO1 exerts many biological activities, including antioxidant activities, anti-inflammatory effects, and interactions with tumor suppressors. Moreover, several recent studies have revealed the promising roles of NQO1 in protecting against cardiovascular damage and related diseases, such as dyslipidemia, atherosclerosis, insulin resistance, and metabolic syndrome. In this review, we discuss recent developments in the molecular regulation and biochemical properties of NQO1, and describe the potential beneficial roles of NQO1 in diseases associated with oxidative stress.

Concurrent Reactive Oxygen Species Generation and Aneuploidy Induction Contribute to Thymoquinone Anticancer Activity

Thymoquinone (TQ) is the main biologically active constituent of Nigella sativa. Many studies have confirmed its anticancer actions. Herein, we investigated the different anticancer activities of, and considered resistance mechanisms to, TQ. MTT and clonogenic data showed TQ’s ability to suppress breast MDA-MB-468 and T-47D proliferation at lower concentrations compared to other cancer and non-transformed cell lines tested (GI₅₀ values ≤ 1.5 µM). Flow-cytometric analyses revealed that TQ consistently induced MDA-MB-468 and T-47D cell-cycle perturbation, specifically inducing pre-G1 populations. In comparison, less sensitive breast MCF-7 and colon HCT-116 cells exhibited only transient increases in pre-G1 events. Annexin V/PI staining confirmed apoptosis induction in MDA-MB-468 and HCT-116 cells, which was continuous in the former and transient in the latter. Experiments revealed the role of reactive oxygen species (ROS) generation and aneuploidy induction in MDA-MB-468 cells within the first 24 h of treatment. The ROS-scavenger NAD(P)H dehydrogenase (quinone 1) (NQO1; DT-diaphorase) and glutathione (GSH) were implicated in resistance to TQ. Indeed, western blot analyses showed that NQO1 is expressed in all cell lines in this study, except those most sensitive to TQ-MDA-MB-468 and T-47D. Moreover, TQ treatment increased NQO1 expression in HCT-116 in a concentration-dependent fashion. Measurement of GSH activity in MDA-MB-468 and HCT-116 cells found that GSH is similarly active in both cell lines. Furthermore, GSH depletion rendered these cells more sensitive to TQ’s antiproliferative actions. Therefore, to bypass putative inactivation of the TQ semiquinone metabolite, the benzylamine analogue was designed and synthesised following modification of TQ’s carbon-3 atom. However, the structural modification negatively impacted potency against MDA-MB-468 cells. In conclusion, we disclose the following: (i) The anticancer activity of TQ may be a consequence of ROS generation and aneuploidy; (ii) Early GSH depletion could substantially enhance TQ’s anticancer activity; (iii) Benzylamine substitution at TQ’s carbon-3 failed to enhance anticancer activity.

Measuring NQO1 Bioactivation Using [2H7]Glucose

Treatment of cancers with β-lapachone causes NAD(P)H: quinone oxidoreductase 1 (NQO1) to generate an unstable hydroquinone that regenerates itself in a futile cycle while producing reactive oxygen species (ROS) in the form of superoxide and subsequently hydrogen peroxide. Rapid accumulation of ROS damages DNA, hyperactivates poly-ADP-ribose polymerase-I, causes massive depletion of NAD+/ATP, and hampers glycolysis. Cells overexpressing NQO1 subsequently die rapidly through an NAD+-keresis mechanism. Assessing changes in glycolytic rates caused by NQO1 bioactivation would provide a means of assessing treatment efficacy, potentially lowering the chemotherapeutic dosage, and reducing off-target toxicities. NQO1-mediated changes in glycolytic flux were readily detected in A549 (lung), MiaPaCa2 (pancreatic), and HCT-116 (colon) cancer cell lines by 2H-NMR after administration of [2H7]glucose. The deuterated metabolic products 2H-lactate and HDO were quantified, and linear relationships with glucose consumption for both products were observed. The higher concentration of HDO compared to 2H-lactate allows for more sensitive measurement of the glycolytic flux in cancer. Gas chromatography-mass spectrometry analysis agreed with the NMR results and confirmed downregulated energy metabolism in NQO1+ cells after β-lapachone treatment. The demonstrated method is ideal for measuring glycolytic rates, the effects of chemotherapeutics that target glycolysis, and has the potential for in vivo translation.

NQO1 protects obese mice through improvements in glucose and lipid metabolism

Chronic nutrient excess leads to metabolic disorders and insulin resistance. Activation of stress-responsive pathways via Nrf2 activation contributes to energy metabolism regulation. Here, inducible activation of Nrf2 in mice and transgenesis of the Nrf2 target, NQO1, conferred protection from diet-induced metabolic defects through preservation of glucose homeostasis, insulin sensitivity, and lipid handling with improved physiological outcomes. NQO1-RNA interaction mediated the association with and inhibition of the translational machinery in skeletal muscle of NQO1 transgenic mice. NQO1-Tg mice on high-fat diet had lower adipose tissue macrophages and enhanced expression of lipogenic enzymes coincident with reduction in circulating and hepatic lipids. Metabolomics data revealed a systemic metabolic signature of improved glucose handling, cellular redox, and NAD+ metabolism while label-free quantitative mass spectrometry in skeletal muscle uncovered a distinct diet- and genotype-dependent acetylation pattern of SIRT3 targets across the core of intermediary metabolism. Thus, under nutritional excess, NQO1 transgenesis preserves healthful benefits.

Insights into the New Cancer Therapy through Redox Homeostasis and Metabolic Shifts

Modest levels of reactive oxygen species (ROS) are necessary for intracellular signaling, cell division, and enzyme activation. These ROS are later eliminated by the body’s antioxidant defense system. High amounts of ROS cause carcinogenesis by altering the signaling pathways associated with metabolism, proliferation, metastasis, and cell survival. Cancer cells exhibit enhanced ATP production and high ROS levels, which allow them to maintain elevated proliferation through metabolic reprograming. In order to prevent further ROS generation, cancer cells rely on more glycolysis to produce ATP and on the pentose phosphate pathway to provide NADPH. Pro-oxidant therapy can induce more ROS generation beyond the physiologic thresholds in cancer cells. Alternatively, antioxidant therapy can protect normal cells by activating cell survival signaling cascades, such as the nuclear factor erythroid 2-related factor 2 (Nrf2)-Kelch-like ECH-associated protein 1 (Keap1) pathway, in response to radio- and chemotherapeutic drugs. Nrf2 is a key regulator that protects cells from oxidative stress. Under normal conditions, Nrf2 is tightly bound to Keap1 and is ubiquitinated and degraded by the proteasome. However, under oxidative stress, or when treated with Nrf2 activators, Nrf2 is liberated from the Nrf2-Keap1 complex, translocated into the nucleus, and bound to the antioxidant response element in association with other factors. This cascade results in the expression of detoxifying enzymes, including NADH-quinone oxidoreductase 1 (NQO1) and heme oxygenase 1. NQO1 and cytochrome b5 reductase can neutralize ROS in the plasma membrane and induce a high NAD⁺/NADH ratio, which then activates SIRT1 and mitochondrial bioenergetics. NQO1 can also stabilize the tumor suppressor p53. Given their roles in cancer pathogenesis, redox homeostasis and the metabolic shift from glycolysis to oxidative phosphorylation (through activation of Nrf2 and NQO1) seem to be good targets for cancer therapy. Therefore, Nrf2 modulation and NQO1 stimulation could be important therapeutic targets for cancer prevention and treatment.

Frequency switching between oscillatory homeostats and the regulation of p53

Homeostasis is an essential concept to understand the stability of organisms and their adaptive behaviors when coping with external and internal assaults. Many hormones that take part in homeostatic control come in antagonistic pairs, such as glucagon and insulin reflecting the inflow and outflow compensatory mechanisms to control a certain internal variable, such as blood sugar levels. By including negative feedback loops homeostatic controllers can exhibit oscillations with characteristic frequencies. In this paper we demonstrate the associated frequency changes in homeostatic systems when individual controllers -in a set of interlocked feedback loops- gain control in response to environmental changes. Taking p53 as an example, we show how Per2, ATM and Mdm2 feedback loops -interlocked with p53- gain individual control in dependence to the level of DNA damage, and how each of these controllers provide certain functionalities in their regulation of p53. In unstressed cells, the circadian regulator Per2 ensures a basic p53 level to allow its rapid up-regulation in case of DNA damage. When DNA damage occurs the ATM controller increases the level of p53 and defends it towards uncontrolled degradation, which despite DNA damage, would drive p53 to lower values and p53 dysfunction. Mdm2 on its side keeps p53 at a high but sub-apoptotic level to avoid premature apoptosis. However, with on-going DNA damage the Mdm2 set-point is increased by HSP90 and other p53 stabilizers leading finally to apoptosis. An emergent aspect of p53 upregulation during cell stress is the coordinated inhibition of ubiquitin-independent and ubiquitin-dependent degradation reactions. Whether oscillations serve a function or are merely a by-product of the controllers are discussed in view of the finding that homeostatic control of p53, as indicated above, does in principle not require oscillatory homeostats.

Curcumin stabilizes p53 by interaction with NAD(P)H:quinone oxidoreductase 1 in tumor-derived cell lines

Curcumin is a natural phytochemical with potent anti-neoplastic properties including modulation of p53. Targeting p53 activity has been suggested as an important strategy in cancer therapy. The purpose of this study was to describe a mechanism by which curcumin restores p53 levels in human cancer cell lines. HeLa, SiHa, CaSki and MDA-MB-231 cells were exposed to curcumin and a pulse and chase and immunoprecipitation assays were performed. Here we showed that curcumin increases the half-life of p53 by a physical interaction between p53-NQO1 (p53 - NAD(P)H:quinone oxidoreductase 1) proteins after treatment with curcumin. Interestingly, the cell viability assay after treatment with curcumin showed that the cytotoxic activity was selectively higher in cervical cancer cells contained wild type p53 but not in breast cancer cells contained mutated p53. The cytotoxic effect of curcumin in cervical cancer cells was related to the complex p53-NQO1 that avoids the interaction between p53 and its negative regulator ubiquitin ligase E6-associated protein (E6AP). Finally, we demonstrated that in pancreatic epithelioid carcinoma cells (PANC1) that are knockout for NQO1, the reestablishment of NQO1 expression can stabilize p53 in presence of curcumin. Collectively, our findings showed that curcumin is necessary to promote the protein interaction of NQO1 with p53, therefore, it increases the half-life of p53, and permits the cytotoxic effect of curcumin in cancer cells containing wild type p53. Our findings suggest that the use of curcumin may reactivate the p53 pathway in cancer cells with p53 wild-type.

NQO1 potentiates apoptosis evasion and upregulates XIAP via inhibiting proteasome-mediated degradation SIRT6 in hepatocellular carcinoma

Background

Our previous study has demonstrated that NAD(P)H: quinone oxidoreductase 1 (NQO1) is significantly upregulated in human liver cancer where it potentiates the apoptosis evasion of liver cancer cell. However, the underlying mechanisms of the oncogenic function of NQO1 in HCC have not been fully elucidated.

Methods

Expression of NQO1, SIRT6, AKT and X-linked inhibitor of apoptosis protein (XIAP) protein were measured by western blotting and immunohistochemistry. Additionally, the interaction between NQO1 and potential proteins were determined by immunoprecipitation assays. Furthermore, the effect of NQO1 and SIRT6 on tumor growth was determined in cell model and orthotopic tumor implantation model.

Results

We found that NQO1 overexpression in HCC enhanced SIRT6 protein stability via inhibiting ubiquitin-mediated 26S proteasome degradation. High level of SIRT6 reduced acetylation of AKT which resulted in increased phosphorylation and activity of AKT. Activated AKT subsequently phosphorylated anti-apoptotic protein XIAP at Ser87 which determined its protein stability. Reintroduction of SIRT6 or AKT efficiently rescued NQO1 knock-out-mediated inhibition of growth and induction of apoptosis. In orthotopic mouse model, NQO1 knock-out inhibited tumor growth and induced apoptosis while this effect was effectively rescued by SIRT6 overexpression or MG132 treatment partially.

Conclusions

Collectively, these results reveal an oncogenic function of NQO1 in sustaining HCC cell proliferation through SIRT6/AKT/XIAP signaling pathway.

Cancer-associated variants of human NQO1: impacts on inhibitor binding and cooperativity

Human NAD(P)H quinone oxidoreductase (DT-diaphorase, NQO1) exhibits negative cooperativity towards its potent inhibitor, dicoumarol. Here, we addressed the hypothesis that the effects of the two cancer-associated polymorphisms (p.R139W and p.P187S) may be partly mediated by their effects on inhibitor binding and negative cooperativity. Dicoumarol stabilized both variants and bound with much higher affinity for p.R139W than p.P187S. Both variants exhibited negative cooperativity towards dicoumarol; in both cases, the Hill coefficient (h) was approximately 0.5 and similar to that observed with the wild-type protein. NQO1 was also inhibited by resveratrol and by nicotinamide. Inhibition of NQO1 by resveratrol was approximately 10,000-fold less strong than that observed with the structurally similar enzyme, NRH quinine oxidoreductase 2 (NQO2). The enzyme exhibited non-cooperative behaviour towards nicotinamide, whereas resveratrol induced modest negative cooperativity (h = 0.85). Nicotinamide stabilized wild-type NQO1 and p.R139W towards thermal denaturation but had no detectable effect on p.P187S. Resveratrol destabilized the wild-type enzyme and both cancer-associated variants. Our data suggest that neither polymorphism exerts its effect by changing the enzyme’s ability to exhibit negative cooperativity towards inhibitors. However, it does demonstrate that resveratrol can inhibit NQO1 in addition to this compound’s well-documented effects on NQO2. The implications of these findings for molecular pathology are discussed.

NQO1: A target for the treatment of cancer and neurological diseases, and a model to understand loss of function disease mechanisms

NAD(P)H quinone oxidoreductase 1 (NQO1) is a multi-functional protein that catalyses the reduction of quinones (and other molecules), thus playing roles in xenobiotic detoxification and redox balance, and also has roles in stabilising apoptosis regulators such as p53. The structure and enzymology of NQO1 is well-characterised, showing a substituted enzyme mechanism in which NAD(P)H binds first and reduces an FAD cofactor in the active site, assisted by a charge relay system involving Tyr-155 and His-161. Protein dynamics play important role in physio-pathological aspects of this protein. NQO1 is a good target to treat cancer due to its overexpression in cancer cells. A polymorphic form of NQO1 (p.P187S) is associated with increased cancer risk and certain neurological disorders (such as multiple sclerosis and Alzheimer´s disease), possibly due to its roles in the antioxidant defence. p.P187S has greatly reduced FAD affinity and stability, due to destabilization of the flavin binding site and the C-terminal domain, which leading to reduced activity and enhanced degradation. Suppressor mutations partially restore the activity of p.P187S by local stabilization of these regions, and showing long-range allosteric communication within the protein. Consequently, the correction of NQO1 misfolding by pharmacological chaperones is a viable strategy, which may be useful to treat cancer and some neurological conditions, targeting structural spots linked to specific disease-mechanisms. Thus, NQO1 emerges as a good model to investigate loss of function mechanisms in genetic diseases as well as to improve strategies to discriminate between neutral and pathogenic variants in genome-wide sequencing studies.

NAD(P)H quinone oxidoreductase (NQO1): an enzyme which needs just enough mobility, in just the right places

NAD(P)H quinone oxidoreductase 1 (NQO1) catalyses the two electron reduction of quinones and a wide range of other organic compounds. Its physiological role is believed to be partly the reduction of free radical load in cells and the detoxification of xenobiotics. It also has non-enzymatic functions stabilising a number of cellular regulators including p53. Functionally, NQO1 is a homodimer with two active sites formed from residues from both polypeptide chains. Catalysis proceeds via a substituted enzyme mechanism involving a tightly bound FAD cofactor. Dicoumarol and some structurally related compounds act as competitive inhibitors of NQO1. There is some evidence for negative cooperativity in quinine oxidoreductases which is most likely to be mediated at least in part by alterations to the mobility of the protein. Human NQO1 is implicated in cancer. It is often over-expressed in cancer cells and as such is considered as a possible drug target. Interestingly, a common polymorphic form of human NQO1, p.P187S, is associated with an increased risk of several forms of cancer. This variant has much lower activity than the wild-type, primarily due to its substantially reduced affinity for FAD which results from lower stability. This lower stability results from inappropriate mobility of key parts of the protein. Thus, NQO1 relies on correct mobility for normal function, but inappropriate mobility results in dysfunction and may cause disease.

Phosphorylation compromises FAD binding and intracellular stability of wild-type and cancer-associated NQO1: Insights into flavo-proteome stability

Over a quarter million of protein phosphorylation sites have been identified so far, although the effects of site-specific phosphorylation on protein function and stability, as well as their possible impact in the phenotypic manifestation in genetic diseases are vastly unknown. We investigated here the effects of phosphorylating S82 in human NADP(H):quinone oxidoreductase 1, a representative example of disease-associated flavoprotein in which protein stability is coupled to the intracellular flavin levels. Additionally, the cancer-associated P187S polymorphism causes inactivation and destabilization of the enzyme. By using extensive in vitro and in silico characterization of phosphomimetic S82D mutations, we showed that S82D locally affected the flavin binding site of the wild-type (WT) and P187S proteins thus altering flavin binding affinity, conformational stability and aggregation propensity. Consequently, the phosphomimetic S82D may destabilize the WT protein intracellularly by promoting the formation of the degradation-prone apo-protein. Noteworthy, WT and P187S proteins respond differently to the phosphomimetic mutation in terms of intracellular stability, further supporting differences in molecular recognition of these two variants by the proteasomal degradation pathway. We propose that phosphorylation could have critical consequences on stability and function of human flavoproteins, important for our understanding of genotype-phenotype relationships in their related genetic diseases.

Natural (and Unnatural) Small Molecules as Pharmacological Chaperones and Inhibitors in Cancer

Mutations causing single amino acid exchanges can dramatically affect protein stability and function, leading to disease. In this chapter, we will focus on several representative cases in which such mutations affect protein stability and function leading to cancer. Mutations in BRAF and p53 have been extensively characterized as paradigms of loss-of-function/gain-of-function mechanisms found in a remarkably large fraction of tumours. Loss of RB1 is strongly associated with cancer progression, although the molecular mechanisms by which missense mutations affect protein function and stability are not well known. Polymorphisms in NQO1 represent a remarkable example of the relationships between intracellular destabilization and inactivation due to dynamic alterations in protein ensembles leading to loss of function. We will review the function of these proteins and their dysfunction in cancer and then describe in some detail the effects of the most relevant cancer-associated single amino exchanges using a translational perspective, from the viewpoints of molecular genetics and pathology, protein biochemistry and biophysics, structural, and cell biology. This will allow us to introduce several representative examples of natural and synthetic small molecules applied and developed to overcome functional, stability, and regulatory alterations due to cancer-associated amino acid exchanges, which hold the promise for using them as potential pharmacological cancer therapies.

Salvia fruticosa Modulates mRNA Expressions and Activity Levels of Xenobiotic Metabolizing CYP1A2, CYP2E1, NQO1, GPx, and GST Enzymes in Human Colorectal Adenocarcinoma HT-29 Cells

Natural products have gained considerable interests because of their use in some industrial areas including nutrition, cosmetic, pharmacy, and medicine. Salvia fruticosa M. (Lamiaceae) is known for its antioxidant, antimicrobial, and antiproliferative activities. Phase I xenobiotic metabolizing enzymes, CYP1A2 and CYP2E1, produce reactive metabolites which are eliminated by the action of phase II enzymes, NQO1, GPx, and glutathione S-transferases (GSTs). In this study, in vitro modulatory effects of S. fruticosa and its major phenolic compound rosmarinic acid (RA) on CYP1A2, CYP2E1, NQO1, GPx, and GSTm1 mRNA expressions and enzyme activities of GPx and GSTs were investigated in HT-29 cells. An mRNA expression analysis revealed that CYP1A2 and CYP2E1 levels were decreased while those of NQO1, GPx, and GSTm1 increased after S. fruticosa and RA treatments. In parallel to gene expressions, enzyme activities of GPx and GSTs by S. fruticosa increased 1.68- and 1.48-fold, respectively. Moreover, RA increased GPx and GSTs activities 1.67- and 1.94-fold, respectively. The results of this preliminary study show that metabolism of xenobiotics may be altered due to changes in the expression and activity of the investigated enzymes by S. fruticosa.

Site-to-site interdomain communication may mediate different loss-of-function mechanisms in a cancer-associated NQO1 polymorphism

Disease associated genetic variations often cause intracellular enzyme inactivation, dysregulation and instability. However, allosteric communication of mutational effects to distant functional sites leading to loss-of-function remains poorly understood. We characterize here interdomain site-to-site communication by which a common cancer-associated single nucleotide polymorphism (c.C609T/p.P187S) reduces the activity and stability in vivo of NAD(P)H:quinone oxidoreductase 1 (NQO1). NQO1 is a FAD-dependent, two-domain multifunctional stress protein acting as a Phase II enzyme, activating cancer pro-drugs and stabilizing p53 and p73α oncosuppressors. We show that p.P187S causes structural and dynamic changes communicated to functional sites far from the mutated site, affecting the FAD binding site located at the N-terminal domain (NTD) and accelerating proteasomal degradation through dynamic effects on the C-terminal domain (CTD). Structural protein:protein interaction studies reveal that the cancer-associated polymorphism does not abolish the interaction with p73α, indicating that oncosuppressor destabilization largely mirrors the low intracellular stability of p.P187S. In conclusion, we show how a single disease associated amino acid change may allosterically perturb several functional sites in an oligomeric and multidomain protein. These results have important implications for the understanding of loss-of-function genetic diseases and the identification of novel structural hot spots as targets for pharmacological intervention.

Mitochondria as a Signaling Hub and Target for Phenoptosis Shutdown

Mitochondria have long been studied as the main energy source and one of the most important generators of reactive oxygen species in the eukaryotic cell. Yet, new data suggest mitochondria serve as a powerful cellular regulator, pathway trigger, and signal hub. Some of these crucial mitochondrial functions appear to be associated with RNP-granules. Deep and versatile involvement of mitochondria in general cellular regulation may be the legacy of parasitic behavior of the ancestors of mitochondria in the host cells. In this regard, we also discuss here the perspectives of using mitochondria-targeted compounds for systemic correction of phenoptotic shifts.

Quercetin as an Emerging Anti-Melanoma Agent: A Four-Focus Area Therapeutic Development Strategy

Replacing current refractory treatments for melanoma with new prevention and therapeutic approaches is crucial in order to successfully treat this aggressive cancer form. Melanoma develops from neural crest cells, which express tyrosinase – a key enzyme in the pigmentation pathway. The tyrosinase enzyme is highly active in melanoma cells and metabolizes polyphenolic compounds; tyrosinase expression thus makes feasible a target for polyphenol-based therapies. For example, quercetin (3,3′,4′,5,7-pentahydroxyflavone) is a highly ubiquitous and well-classified dietary polyphenol found in various fruits, vegetables, and other plant products including onions, broccoli, kale, oranges, blueberries, apples, and tea. Quercetin has demonstrated antiproliferative and proapoptotic activity in various cancer cell types. Quercetin is readily metabolized by tyrosinase into various compounds that promote anticancer activity; additionally, given that tyrosinase expression increases during tumorigenesis, and its activity is associated with pigmentation changes in both early- and late-stage melanocytic lesions, it suggests that quercetin can be used to target melanoma. In this review, we explore the potential of quercetin as an anti-melanoma agent utilizing and extrapolating on evidence from previous in vitro studies in various human malignant cell lines and propose a “four-focus area strategy” to develop quercetin as a targeted anti-melanoma compound for use as either a preventative or therapeutic agent. The four areas of focus include utilizing quercetin to (i) modulate cellular bioreduction potential and associated signaling cascades, (ii) affect transcription of relevant genes, (iii) regulate epigenetic processes, and (iv) develop effective combination therapies and delivery modalities/protocols. In general, quercetin could be used to exploit tyrosinase activity to prevent, and/or treat, melanoma with minimal additional side effects.

Activation of NQO1 in NQO1*2 polymorphic human leukemic HL-60 cells by diet-derived sulforaphane

Background

The NAD(P)H: quinone oxidoreductase (NQO1) confers protection against semiquinones and also elicits oxidative stress. The C609T polymorphism of the NQO1 gene, designated NQO1*2, significantly reduces its enzymatic activity due to rapid degradation of protein. Since down regulation of NQO1 mRNA expression correlates with increased susceptibility for developing different types of cancers, we investigated the link between leukemia and the NQO1*2 genotype by mining a web-based microarray dataset, ONCOMINE. Phytochemicals prevent DNA damage through activation of phase II detoxification enzymes including NQO1. Whether NQO1 expression/activity in leukemia cells that carry the labile NQO1*2 genotype can be induced by broccoli-derived phytochemical sulforaphane (SFN) is currently unknown.

Methods and Results

The ONCOMINE query showed that: (1) acute lymphoblastic leukemia and chronic myelogenous leukemia are associated with reduced NQO1 levels, and (2) under-expressed NQO1 was found in human HL-60 leukemia cell line containing the heterozygous NQO1*2 polymorphism. We examined induction of NQO1 activity/expression by SFN in HL-60 cells. A dose-dependent increase in NQO1 level/activity is accompanied by upregulation of the transcription factor, Nrf2, following 1–10 μM SFN treatment. Treatment with 25 µM SFN drastically reduced NQO1 levels, inhibited cell proliferation, caused sub-G₁ cell arrest, and induced apoptosis, and a decrease in the levels of the transcription factor, nuclear factor-κB (NFκB).

Conclusions

Up to 10 μM of SFN increases NQO1 expression and suppresses HL-60 cell proliferation whereas ≥ 25 μM of SFN induces apoptosis in HL-60 cells. Further, SFN treatment restores NQO1 activity/levels in HL-60 cells expressing the NQO1*2 genotype.

DNA damage signalling barrier, oxidative stress and treatment-relevant DNA repair factor alterations during progression of human prostate cancer

The DNA damage checkpoints provide an anti-cancer barrier in diverse tumour types, however this concept has remained unexplored in prostate cancer (CaP). Furthermore, targeting DNA repair defects by PARP1 inhibitors (PARPi) as a cancer treatment strategy is emerging yet requires suitable predictive biomarkers. To address these issues, we performed immunohistochemical analysis of multiple markers of DNA damage signalling, oxidative stress, DNA repair and cell cycle control pathways during progression of human prostate disease from benign hyperplasia, through intraepithelial neoplasia to CaP, complemented by genetic analyses of TMPRSS2-ERG rearrangement and NQO1, an anti-oxidant factor and p53 protector. The DNA damage checkpoint barrier (γH2AX, pATM, p53) mechanism was activated during CaP tumorigenesis, albeit less and with delayed culmination compared to other cancers, possibly reflecting lower replication stress (slow proliferation despite cases of Rb loss and cyclin D1 overexpression) and progressive loss of ATM activator NKX3.1. Oxidative stress (8-oxoguanine lesions) and NQO1 increased during disease progression. NQO1 genotypes of 390 men did not indicate predisposition to CaP, yet loss of NQO1 in CaP suggested potential progression-opposing tumour suppressor role. TMPRSS2-ERG rearrangement and PTEN loss, events sensitizing to PARPi, occurred frequently along with heterogeneous loss of DNA repair factors 53BP1, JMJD1C and Rev7 (all studied here for the first time in CaP) whose defects may cause resistance to PARPi. Overall, our results reveal an unorthodox DNA damage checkpoint barrier scenario in CaP tumorigenesis, and provide novel insights into oxidative stress and DNA repair, with implications for biomarker guidance of future targeted therapy of CaP.

Using DNA devices to track anticancer drug activity

It is beneficial to develop systems that reproduce complex reactions of biological systems while maintaining control over specific factors involved in such processes. We demonstrated a DNA device for following the repair of DNA damage produced by a redox-cycling anticancer drug, beta-lapachone (β-lap). These chips supported ß-lap-induced biological redox cycle and tracked subsequent DNA damage repair activity with redox-modified DNA monolayers on gold. We observed drug-specific changes in square wave voltammetry from these chips at therapeutic ß-lap concentrations of high statistical significance over drug-free control. We also demonstrated a high correlation of this change with the specific ß-lap-induced redox cycle using rational controls. The concentration dependence of ß-lap revealed significant signal changes at levels of high clinical significance as well as sensitivity to sub-lethal levels of ß-lap. Catalase, an enzyme decomposing peroxide, was found to suppress DNA damage at a NQO1/catalase ratio found in healthy cells, but was clearly overcome at a higher NQO1/catalase ratio consistent with cancer cells. We found that it was necessary to reproduce key features of the cellular environment to observe this activity. Thus, this chip-based platform enabled tracking of ß-lap-induced DNA damage repair when biological criteria were met, providing a unique synthetic platform for uncovering activity normally confined to inside cells.

A direct interaction between NQO1 and a chemotherapeutic dimeric naphthoquinone

BACKGROUND

Multimeric naphthoquinones are redox-active compounds that exhibit antineoplastic, antiprotozoal, and antiviral activities. Due to their multimodal effect on perturbation of cellular oxidative state, these compounds hold great potential as therapeutic agents against highly proliferative neoplastic cells. In our previous work, we developed a series of novel dimeric naphthoquinones and showed that they were selectively cytotoxic to human acute myeloid leukemia (AML), breast and prostate cancer cell lines. We subsequently identified the oxidoreductase NAD(P)H dehydrogenase, quinone 1 (NQO1) as the major target of dimeric naphthoquinones and proposed a mechanism of action that entailed induction of a futile redox cycling.

RESULTS

Here, for the first time, we describe a direct physical interaction between the bromohydroxy dimeric naphthoquinone E6a and NQO1. Moreover, our studies reveal an extensive binding interface between E6a and the isoalloxazine ring of the flavin adenine dinucleotide (FAD) cofactor of NQO1 in addition to interactions with protein side chains in the active site. We also present biochemical evidence that dimeric naphthoquinones affect the redox state of the FAD cofactor of NQO1. Comparison of the mode of binding of E6a with those of other chemotherapeutics reveals unique characteristics of the interaction that can be leveraged in future drug optimization efforts.

CONCLUSION

The first structure of a dimeric naphthoquinone-NQO1 complex was reported, which can be used for design and synthesis of more potent next generation dimeric naphthoquinones to target NQO1 with higher affinity and specificity.

Contribution of ellagic acid on the antioxidant potential of medicinal plant Epilobium hirsutum

In the present study, the possible role of ellagic acid (EA) on antioxidant potential of Epilobium hirsutum (EH) in rat liver was investigated. Wistar rats were intraperitoneally treated with 37.5 mg/kg of EH and 10 mg/kg of EA for 9 days. Effects of EH and EA on antioxidant [glutathione peroxidase (GPx) and superoxide dismutases (SOD)] and Phase II [NADPH quinone oxidoreductase 1 (NQO1) and glutathione S-transferases (GSTs)] enzyme activities, as well as protein and mRNA expressions of those, were investigated. Polyphenolic content of EH was determined by LC-MS/MS analysis. EH and EA injection to rats resulted in a significant increase of NQO1 (3.6-fold and 4.7-fold), GPx (1.45-fold), and SOD (1.34-fold and 1.27-fold) enzyme activities, whereas total GST (46% and 57%) and its isoforms,and GST mu (57% and 72%), and GST theta (60% and 68%) activities were significantly decreased. Western-blot and qRT-PCR analysis showed that NQO1 and GPx protein and mRNA expressions were increased significantly (P < 0.0001), whereas GST mu and GST theta were significantly decreased (P < 0.0001).

Can dicoumarol be used as a gonad-safe anticancer agent: an in vitro and in vivo experimental study

STUDY HYPOTHESIS

Dicoumarol (DC) has potential for use as a gonad-safe anticancer agent.

STUDY FINDING

DC altered cell proliferation, decreased viability and increased apoptosis in Vero and MCF-7 cell lines but did not show any toxic effect on mouse ovarian tissues and developing oocytes in vitro and in vivo.

WHAT IS KNOWN ALREADY

DC suppresses cell proliferation and increases apoptosis in various cancer cells such as breast, urogenital and melanoma. DC has also been reported to alter the anticancer effects of several chemotherapeutics, including cisplatin, gemcitabine and doxorubicin in prostate, liver and uroepithelial cancer cells, respectively.

STUDY DESIGN, SAMPLES/MATERIALS, METHODS

Vero (African green monkey kidney epithelial cells) and MCF-7 (human cancerous breast epithelial cells) cell lines and mouse granulosa cells isolated from 21-day-old female BALB/c mice (n = 21) were used to assess the effects of DC (10, 50, 100 and 200 µm) for 24 and 48 h on cell proliferation, viability and apoptotic cell death. In vivo experiments were performed with a single i.p. injection of 32 mg/kg DC in 21-day-old female BALB/c mice (n = 12). Following 48 h, animals were sacrificed by cervical dislocation and histological sections of isolated ovaries were evaluated for apoptosis. Viability assays were based on the trypan blue dye exclusion method and an automated cell counter device was used. Terminal deoxynucleotidyltransferase-mediated dUTP nick-end labelling (TUNEL) and Annexin-V immunofluorescence were assessed by 3D confocal microscopy to address apoptotic cell death. We also assessed whether DC inhibits cell proliferation and viability through NQO1 [NAD(P)H Quinone Oxidoreductase 1], an intracellular inhibitor of reactive oxygen species (ROS). The meiotic spindle and chromosomes were studied in mouse oocytes by α-β-tubulin and 7-aminoactinomycine D (7-AAD) immunostaining in vitro and in vivo.

MAIN RESULTS AND THE ROLE OF CHANCE

DC does not block oocyte maturation and no significant alteration was noted in meiotic spindle or chromosome morphology in metaphase-II (M-II) stage oocytes following DC treatment in vitro or in vivo. In contrast, exposure to DC for 24 h suppressed cell proliferation (P = 0.026 at 200 µm), decreased viability (P = 0.002 at 200 µm) and increased apoptosis (P = 0.048 at 100 µm) in Vero and MCF-7 cell lines, compared with controls. These changes were not related to intracellular NQO1 levels. Mouse granulosa cells were unaffected by 50 or 100 µm DC treatment for 24 and 48 h in vitro. DC treatment in vivo did not alter the number of primordial follicles or the ratio of apoptosis in primordial, primary and secondary follicles, as well as in antral follicles, compared with the controls.

LIMITATIONS, REASONS FOR CAUTION

DC was tested for ovarian toxicity only in isolated mouse oocytes/ovaries and healthy BALB/c mice. No cancer formation was used as an in vivo test model. The possibility that DC may potentiate ovarian toxicity when combined with traditional chemotherapeutic agents, such as mitomycin-C, cisplatin, gemcitabine and doxorubicin, must be taken into account, as DC is known to alter their effects in some cancer cells.

WIDER IMPLICATIONS OF THE FINDINGS

The present study evaluated, for the first time, the effect of DC on ovarian tissue. The results suggested that DC is not toxic to ovarian tissues and developing oocytes; therefore, DC should be assessed further as a potential anticancer agent when female fertility preservation is a concern.

LARGE SCALE DATA

N/A.

STUDY FUNDING AND COMPETING INTERESTS

This work includes data from dissertation thesis entitled 'Effects of dicoumarol on mitotic and meiotic cells as an anticancer agent' by DA, 2014 and was partly supported by The National Scientific and Technological Research Council of Turkey (SBAG-109S415) to AC, OC and SO. The authors confirm that this article content presents no conflicts of interest.

Implications of NQO1 in cancer therapy

NAD(P)H

quinone oxidoreductase (NQO1), an obligatory two-electron reductase, is a ubiquitous cytosolic enzyme that catalyzes the reduction of quinone substrates. The NQO1- mediated two-electron reduction of quinones can be either chemoprotection/detoxification or a chemotherapeutic response, depending on the target quinones. When toxic quinones are reduced by NQO1, they are conjugated with glutathione or glucuronic acid and excreted from the cells. Based on this protective effect of NQO1, the use of dietary compounds to induce the expression of NQO1 has emerged as a promising strategy for cancer prevention. On the other hand, NQO1-mediated two-electron reduction converts certain quinone compounds (such as mitomycin C, E09, RH1 and -lapachone) to cytotoxic agents, leading to cell death. It has been known that NQO1 is expressed at high levels in numerous human cancers, including breast, colon, cervix, lung, and pancreas, as compared with normal tissues. This implies that tumors can be preferentially damaged relative to normal tissue by cytotoxic quinone drugs. Importantly, NQO1 has been shown to stabilize many proteins, including p53 and p33ING1b, by inhibiting their proteasomal degradation. This review will summarize the biological roles of NQO1 in cancer, with emphasis on recent findings and the potential of NQO1 as a therapeutic target for the cancer therapy.

Clinical Significance of the NQO1 C609T Polymorphism in Non Small Cell Lung Adenocarcinoma Patients

NAD(P)H

quinone oxidoreductase 1 (NQO1) is part of the antioxidant defence system involved in detoxification. This study aimed to analyze the influence of NQO1 (C609T) genetic polymorphism in non small cell lung cancer (NSCLC)as a putative risk factor.

MATERIALS AND METHODS

Present study included 100 cases of NSCLC (adenocarcinoma) patients and 100 age and sex matched healthy controls. NQO1 (C609T) genotyping was performed by allele specific PCR for assessment of putative associations with clinical outcome and genotypes of. The association of the polymorphism with the survival of NSCLC patients' was analyzed by Kaplan-Meier method.

RESULTS

In Indian NSCLC (adenocarcinoma) patients increased risk of developing NSCLC was found to be associated with NQO1 609TT genotype [OR 3.68(0.90-14.98), RR 2.04(0.78-5.31)] for CT [OR 2.91(1.58- 5.34), RR 1.74(1.23-2.44) p= 0.0005 for CT], for CT+TT [ OR 3.26(1.82-5.82), RR 1.87(1.34-2.61) p<0.0001 for CT+TT]. A significant difference (p=0.0009) was observed in genotype distribution among cases and healthy controls. Patients with CT+TT genotype exhibited a significant poor overall survival compared with patients displaying homozygous CC genotype (p=0.03) and when survival independently compared with CC, TT and CT genotype was also found to be significantly associated (p=0.02). Overall median survival times were CT 6.0 months, TT 8.2 months, and CT + TT (6.4 months)].

CONCLUSIONS

The present study revealed that NQO1 CT, TT and CT+TT genotypes may be associated with clinical outcome and risk of developing NSCLC in the Indian population.

NQO1 suppresses NF-κB-p300 interaction to regulate inflammatory mediators associated with prostate tumorigenesis

NADPH reductase

NAD(P)H

quinone oxidoreductase 1 (NQO1) is needed to maintain a cellular pool of antioxidants, and this enzyme may contribute to tumorigenesis on the basis of studies in NQO1-deficient mice. In this work, we sought deeper insights into how NQO1 contributes to prostate carcinogenesis, a setting in which oxidative stress and inflammation are established contributors to disease development and progression. In the TRAMP mouse model of prostate cancer, NQO1 was highly expressed in tumor cells. NQO1 silencing in prostate cancer cells increased levels of nuclear IKKα and NF-κB while decreasing the levels of p53, leading to interactions between NF-κB and p300 that reinforce survival signaling. Gene expression analysis revealed upregulation of a set of immune-associated transcripts associated with inflammation and tumorigenesis in cells in which NQO1 was attenuated, with IL8 confirmed functionally in cell culture as one key NQO1-supported cytokine. Notably, NQO1-silenced prostate cancer cells were more resistant to androgen deprivation. Furthermore, NQO1 inhibition increased migration, including under conditions of androgen deprivation. These results reveal a molecular link between NQO1 expression and proinflammatory cytokine signaling in prostate cancer. Furthermore, our results suggest that altering redox homeostasis through NQO1 inhibition might promote androgen-independent cell survival via opposing effects on NF-κB and p53 function.

The Saccharomyces cerevisiae quinone oxidoreductase Lot6p: stability, inhibition and cooperativity

Lot6p (EC 1.5.1.39; Ylr011wp) is the sole quinone oxidoreductase in the budding yeast, Saccharomyces cerevisiae. Using hexahistidine tagged, recombinant Lot6p, we determined the steady-state enzyme kinetic parameters with both NADH and NADPH as electron donors; no cooperativity was observed with these substrates. The NQO1 inhibitor curcumin, the NQO2 inhibitor resveratrol, the bacterial nitroreductase inhibitor nicotinamide and the phosphate mimic vanadate all stabilise the enzyme towards thermal denaturation as judged by differential scanning fluorimetry. All except vanadate have no observable effect on the chemical cross-linking of the two subunits of the Lot6p dimer. These compounds all inhibit Lot6p's oxidoreductase activity, and all except nicotinamide exhibit negative cooperativity. Molecular modelling suggests that curcumin, resveratrol and nicotinamide all bind over the isoalloxazine ring of the FMN cofactor in Lot6p. Resveratrol was predicted to contact an α-helix that links the two active sites. Mutation of Gly-142 (which forms part of this helix) to serine does not greatly affect the thermal stability of the enzyme. However, this variant shows less cooperativity towards resveratrol than the wild type. This suggests a plausible hypothesis for the transmission of information between the subunits and, thus, the molecular mechanism of negative cooperativity in Lot6p.

The two common polymorphic forms of human NRH-quinone oxidoreductase 2 (NQO2) have different biochemical properties

There are two common forms of NRH-quinone oxidoreductase 2 (NQO2) in the human population resulting from SNP rs1143684. One has phenylalanine at position 47 (NQO2-F47) and the other leucine (NQO2-L47). Using recombinant proteins, we show that these variants have similar steady state kinetic parameters, although NQO2-L47 has a slightly lower specificity constant. NQO2-L47 is less stable towards proteolytic digestion and thermal denaturation than NQO2-F47. Both forms are inhibited by resveratrol, but NQO2-F47 shows negative cooperativity with this inhibitor. Thus these data demonstrate, for the first time, clear biochemical differences between the variants which help explain previous biomedical and epidemiological findings.

Flavins and flavoproteins: applications in medicine

The potential of flavoproteins as targets of pharmacological treatments is immense. In this review we present an overview of the current research progress on medical interventions based on flavoproteins with a special emphasis on cancer, infectious diseases, and neurological disorders.

Epilobium hirsutum alters xenobiotic metabolizing CYP1A1, CYP2E1, NQO1 and GPx activities, mRNA and protein levels in rats

CONTEXT

Natural products have attracted increasing interests due to their use in flavoring, nutrition, cosmetics, pharmacy and medicine. Epilobium hirsutum L. (Onagraceae) is known for its analgesic, antimicrobial, and antiproliferative activity. CYP1A1 and CYP2E1, xenobiotic metabolizing enzymes, serve as a metabolic activation route yielding reactive metabolites that are eliminated by the action of NQO1 and glutathione peroxidase (GPx) enzymes.

OBJECTIVE

This study investigated in vivo effects of Epilobium hirsutum (EH) on CYP2E1, CYP1A1, NQO1 and GPx activities, protein and mRNA expressions in liver.

MATERIALS AND METHODS

Male Wistar Albino rats were injected with EH at a dose of 37.5 mg/kg i.p. daily for 9 d. CYP2E1, CYP1A1, NQO1 and GPx activities, protein and mRNA levels were determined by enzyme assays, Western blotting and qPCR, respectively.

RESULTS

CYP1A1 associated ethoxyresorufin-O-deethylase activity of control and EH-treated animals were found as 6.54 ± 1.21 and 4.48 ± 1.67 nmol/min/mg, respectively. CYP2E1 associated aniline 4-hydroxylase of control and EH group were 0.537 ± 0.011 and 0.109 ± 0.01 nmol/min/mg, respectively. However, EH treatment increased the GPx and NQO1 activities from 0.069 ± 0.015 to 0.107 ± 0.026 nmol/min/mg and from 163.34 ± 92 to 588.3 ± 14 nmol/min/mg, respectively. Furthermore, protein and mRNA expression analysis revealed that CYP1A1 and CYP2E1 levels were decreased while those of NQO1 and GPx increased after EH treatment.

DISCUSSION AND CONCLUSION

Our current data suggest that the metabolism of xenobiotics, including drugs, may be altered due to changes in the expression and activity of these proteins by EH.

Polymorphisms in oxidative stress-related genes and mortality in breast cancer patients--potential differential effects by radiotherapy?

We assessed whether variants in 22 oxidative stress-related genes are associated with mortality of breast cancer patients and whether the associations differ according to radiotherapy. Using a prospective cohort of 1348 postmenopausal breast cancer patients, we estimated hazard ratios (HR) and 95% confidence intervals (CI) for 109 single nucleotide polymorphisms (SNPs) using Cox proportional hazards regression. Validation of results was attempted using two Scandinavian studies. Eleven SNPs in MT2A, NFE2L2, NQO1, PRDX1, and PRDX6 were significantly associated with overall mortality after a median follow-up of 5.7 years. Three SNPs in NQO1 (rs2917667) and in PRDX6 (rs7314, rs4916362) were consistently associated with increased risk of dying across all three study populations (pooled: HRNQO1_rs2917667 1.20, 95% CI 1.00-1.44, p = 0.051; HRPRDX6_rs7314 1.16, 95% CI 1.00-1.35, p = 0.056, HRPRDX6_rs4916362 1.14 95% CI 1.00-1.32, p = 0.062). Potential effect modification by radiotherapy was found for CAT_rs769218. In conclusion, genetic variants in NQO1 and PRDX6 may modify breast cancer prognosis.

NAD(P)H:quinone oxidoreductase 1 is induced by progesterone in cardiomyocytes

NAD(P)H: quinone oxidoreductase 1 (NQO1) is a ubiquitous flavoenzyme that catalyzes two-electron reduction of various quinones by utilizing NAD(P)H as an electron donor. Our previous study found that progesterone (PG) can protect cardiomyocytes from apoptosis induced by doxorubicin (Dox). Microarray analyses of genes induced by PG had led to the discovery of induction of NQO1 mRNA. We report here that PG induces NQO1 protein and its activity in a dose-dependent manner. Whereas NQO1 is well known as a target gene of Nrf2 transcription factor due to the presence of antioxidant response element (ARE) in the promoter, PG did not activate the ARE, suggesting Nrf2-independent induction of NQO1. To address the role of NQO1 induction in PG-induced cytoprotection, we tested the effect of NQO1 inducer β-naphthoflavone and inhibitor dicoumarol. Induction of NQO1 by β-naphthoflavone decreased Dox-induced apoptosis and potentiated the protective effect of PG as measured by caspase-3 activity. PG-induced NQO1 activity was inhibited with dicoumarol, which did not affect PG-induced cytoprotection. Dicoumarol treatment alone potentiated Dox-induced caspase-3 activity. These data suggest that while NQO1 plays a role in PG-induced cytoprotection, there are additional components contributing to PG-induced cytoprotection.

A mutually inhibitory feedback loop between the 20S proteasome and its regulator, NQO1

NAD(P)H:quinone-oxidoreductase-1 (NQO1) is a cytosolic enzyme that catalyzes the reduction of various quinones using flavin adenine dinucleotide (FAD) as a cofactor. NQO1 has been also shown to rescue proteins containing intrinsically unstructured domains, such as p53 and p73, from degradation by the 20S proteasome through an unknown mechanism. Here, we studied the nature of interaction between NQO1 and the 20S proteasome. Our study revealed a double negative feedback loop between NQO1 and the 20S proteasome, whereby NQO1 prevents the proteolytic activity of the 20S proteasome and the 20S proteasome degrades the apo form of NQO1. Furthermore, we demonstrate, both in vivo and in vitro, that NQO1 levels are highly dependent on FAD concentration. These observations suggest a link between 20S proteolysis and the metabolic cellular state. More generally, the results may represent a regulatory mechanism by which associated cofactors dictate the stability of proteins, thus coordinating protein levels with the metabolic status.

Genetic polymorphisms of NQO1, CYP1A1 and TPMT and susceptibility to acute lymphoblastic leukemia in a Tunisian population

Acute lymphoblastic leukemia (ALL) is the major pediatric cancer in developed countries. The etiology of ALL remains poorly understood, with few established environmental risk factors. These risks were influenced by co-inheritance of multiple low-risk genetic polymorphisms such as variants within cytochrome P450A1 (CYP1A1), NADPH: quinone oxidoreductase (NQO1) and Thiopurine methyltransferase (TPMT) genes. In this work, we conduct a case-control study to assess the impact of CYP1A1*2A (CYP1A1 T6235C); NQO1*2 (NQO1 C609T); TPMT*2 (TPMT G238C) and TPMT A719G polymorphisms on the risk of developing ALL. The frequencies of TPMT*2, TPMT A719G, NQO1*2 and CYP1A1*2 variants were examined in 100 patients with ALL and 106 healthy controls by allele specific PCR and/or PCR-RFLP methods using blood samples. We have found that NQO1 609CT genotype was overrepresented in patients and was associated with an aggravating effect compared to the reference group with NQO1 609CC genotype (p = 0.028, OR = 1.41; CI 95 %: 1.04-1.93). However, TPMT*2, TPMT 719*G and CYP1A1*2 variants did not appear to influence ALL susceptibility (p > 0.05). Moreover we have not found a significant correlation between the studied variants and Bcr-Abl transcript. In conclusion we retain that leukemogenesis of ALL is associated with carcinogens metabolism and consequently related to environmental exposures.

Impairment of antioxidant defenses as a contributor to arsenite-induced cell transformation

Arsenite (As) causes transformation of human osteogenic sarcoma cells (HOS) when applied continuously at low doses (0.1-0.5 μM) during 8-weeks of exposure. However, the mechanisms by which As transforms human cells are not known. We investigated whether alterations occurred in gene expression and protein levels of antioxidant defense proteins, such as superoxide dismutase 1 (SOD1) and ferritin. In comparison to control HOS cells, 0.1 μM As induced greater cell proliferation and decreased anti-oxidant defenses. The tumor suppressor protein p53 was also decreased at both mRNA and protein levels. Further, pig3 (p53-induced-gene 3), a homolog of NQO1 (NADPH quinone oxidoreductase 1), was also down-regulated after 8 weeks of As challenge. The treatment of HOS cells with dicumarol, a NQO1 inhibitor, caused a dose-dependent decline in p53 protein levels, proving the effect of an antioxidant enzyme on p53 expression and, potentially, down-stream processes. Caffeic acid phenethyl ester, an antioxidant, prevented the As-induced decreases in SOD1, p53, and ferritin mRNA and protein levels. SOD1, p53 and ferritin levels were inversely related to As-induced cell proliferation. Cumulatively, these results strongly suggest that impairment in antioxidant defenses contributes to As-induced human cell transformation and that the p53 pathway is involved in the process.

Osteopontin is an endogenous modulator of the constitutively activated phenotype of pulmonary adventitial fibroblasts in hypoxic pulmonary hypertension

Increased cell proliferation and migration, of several cell types are key components of vascular remodeling observed in pulmonary hypertension (PH). Our previous data demonstrate that adventitial fibroblasts isolated from pulmonary arteries of chronically hypoxic hypertensive calves (termed PH-Fibs) exhibit a "constitutively activated" phenotype characterized by high proliferative and migratory potential. Osteopontin (OPN) has been shown to promote several cellular activities including growth and migration in cancer cells. We thus tested the hypothesis that elevated OPN expression confers the "activated" highly proproliferative and promigratory/invasive phenotype of PH-Fibs. Our results demonstrate that, both in vivo and ex vivo, PH-Fibs exhibited increased expression of OPN, as well as its cognate receptors, α(V)β(3) and CD44, compared with control fibroblasts (CO-Fibs). Augmented OPN expression in PH-Fibs corresponded to their high proliferative, migratory, and invasive properties and constitutive activation of ERK1/2 and AKT signaling. OPN silencing via small interfering RNA or sequestering OPN production by specific antibodies led to decreased proliferation, migration, invasion, and attenuated ERK1/2, AKT phosphorylation in PH-Fibs. Furthermore, increasing OPN levels in CO-Fibs via recombinant OPN resulted in significant increases in their proliferative, migratory, and invasive capabilities to the levels resembling those of PH-Fibs. Thus our data suggest OPN as an essential contributor to the activated (highly proliferative, migratory, and proinvasive) phenotype of pulmonary adventitial fibroblasts in hypoxic PH.

Benzene toxicity: The role of the susceptibility factor NQO1 in bone marrow endothelial cell signaling and function

The homozygous NQO1*2 polymorphism results in a null NQO1 phenotype and is a susceptibility factor for occupational benzene poisoning. NQO1 plays an important role in detoxification of benzene-derived quinones but plays a role in numerous other non-metabolic cellular functions. NQO1 is expressed in endothelial cells of bone marrow which form the vascular stem cell niche important in stem cell homing and mobilization. We therefore employed a transformed human bone marrow endothelial cell (HBMEC) line to define the effects of compromising NQO1 on endothelial function. Either inhibition or knockdown of NQO1 led to decreased expression of the adhesion molecules E-selectin, VCAM-1 and ICAM-1 and decreased functional adhesion of CD34+ progenitor cells after TNFα stimulation. Suicide inhibition or knockdown of NQO1 decreased NFκB p105 precursor and NFκB p50 subunit levels as well as leading to decreased nuclear levels of NFκB phospho-p65. An additional function of endothelial cells is tube formation and angiogenesis which was inhibited by the benzene metabolite hydroquinone suggesting that endothelial function may be affected at multiple levels after exposure of NQO1*2 polymorphic individuals to benzene. These data demonstrate that NQO1 plays an upstream role in NFκB signaling and adhesion molecule expression in HBMEC and that NQO1 has important regulatory effects in its own right in addition to being a marker for Nrf-2 activation. Metabolic susceptibility factors such as NQO1 have roles in addition to detoxification of reactive intermediates and interrogation of these novel roles can inform both mechanisms of toxicity and human risk assessment.

Influence of cell cycle on responses of MCF-7 cells to benzo[a]pyrene

Background

Benzo[a]pyrene (BaP) is a widespread environmental genotoxic carcinogen that damages DNA by forming adducts. This damage along with activation of the aryl hydrocarbon receptor (AHR) induces complex transcriptional responses in cells. To investigate whether human cells are more susceptible to BaP in a particular phase of the cell cycle, synchronised breast carcinoma MCF-7 cells were exposed to BaP. Cell cycle progression was analysed by flow cytometry, DNA adduct formation was assessed by ³²P-postlabeling analysis, microarrays of 44K human genome-wide oligos and RT-PCR were used to detect gene expression (mRNA) changes and Western blotting was performed to determine the expression of some proteins, including cytochrome P450 (CYP) 1A1 and CYP1B1, which are involved in BaP metabolism.

Results

Following BaP exposure, cells evaded G1 arrest and accumulated in S-phase. Higher levels of DNA damage occurred in S- and G2/M- compared with G0/G1-enriched cultures. Genes that were found to have altered expression included those involved in xenobiotic metabolism, apoptosis, cell cycle regulation and DNA repair. Gene ontology and pathway analysis showed the involvement of various signalling pathways in response to BaP exposure, such as the Catenin/Wnt pathway in G1, the ERK pathway in G1 and S, the Nrf2 pathway in S and G2/M and the Akt pathway in G2/M. An important finding was that higher levels of DNA damage in S- and G2/M-enriched cultures correlated with higher levels of CYP1A1 and CYP1B1 mRNA and proteins. Moreover, exposure of synchronised MCF-7 cells to BaP-7,8-diol-9,10-epoxide (BPDE), the ultimate carcinogenic metabolite of BaP, did not result in significant changes in DNA adduct levels at different phases of the cell cycle.

Conclusions

This study characterised the complex gene response to BaP in MCF-7 cells and revealed a strong correlation between the varying efficiency of BaP metabolism and DNA damage in different phases of the cell cycle. Our results suggest that growth kinetics within a target-cell population may be important determinants of susceptibility and response to a genotoxic agent.

Redox modulation of p53: mechanisms and functional significance

The tumor suppressor protein p53 functions as a stress-responsive transcription factor. In response to oxidative, nitrosative, and electrophilic insults, p53 undergoes post-translational modifications, such as oxidation and covalent modification of cysteines, nitration of tyrosines, acetylation of lysines, phosphorylation of serine/threonine residues, etc. Because p53 plays a vital role in the transcriptional regulation of genes encoding proteins involved in a wide spectrum of biochemical processes including DNA repair, cell-cycle regulation, and programmed cell death, the redox-modification of p53 appears to be an important determinant of cell fate. This review highlights the redox regulation of p53 and its consequences on cellular function.

Ubiquitin proteasomal pathway mediated degradation of p53 in melanoma

Ubiquitin proteasomal pathway (UPP) is the principle mechanism for protein catabolism and affects cellular processes critical for survival and proliferation. Levels of tumor suppressor protein p53 are very low in cells due to its rapid turnover by UPP-mediated degradation. While p53 is mutated in human cancers, most human melanomas maintain wild-type conformation. In this study, to investigate the effects of UPP inhibitor invitro and in vivo, we used a genetically-engineered mouse model (GEMM) that has the same genetic alterations as those of human melanomas. Melanoma cells were established from mouse tumors and named 8B20 cells. Treatment of 8B20 cells with the UPP inhibitors, MG132 and clasto-lactacystin-β-lactone, led to an increase in levels of p53 while treatment with non-proteasomal inhibitors did not alter p53 levels. UPP inhibitors induced formation of heavy molecular weight ubiquitinated proteins, a hallmark of UPP inhibition, and p53-specific poly-ubiquitinated products in 8B20 cells. To further decipher the mechanism of p53 stabilization, we investigated half-life of p53 in cells treated with cycloheximide to block de novo protein synthesis. Treatment of 8B20 cells with MG132 led to an increase in the half-life of p53. Further analysis revealed that p53 stabilization was not mediated by phosphorylation of Ser-15 and Ser-20 residues. In vivo studies showed that MG132 induced p53 overexpression and reduced tumor growth, suggesting an important role of p53 stabilization in controlling melanoma. Taken together, our studies provide a proof of principle for using a GEMM to address the mechanisms of action and efficacy of melanoma treatment.

In vitro gene regulatory networks predict in vivo function of liver

BACKGROUND

Evolution of toxicity testing is predicated upon using in vitro cell based systems to rapidly screen and predict how a chemical might cause toxicity to an organ in vivo. However, the degree to which we can extend in vitro results to in vivo activity and possible mechanisms of action remains to be fully addressed.

RESULTS

Here we use the nitroaromatic 2,4,6-trinitrotoluene (TNT) as a model chemical to compare and determine how we might extrapolate from in vitro data to in vivo effects. We found 341 transcripts differentially expressed in common among in vitro and in vivo assays in response to TNT. The major functional term corresponding to these transcripts was cell cycle. Similarly modulated common pathways were identified between in vitro and in vivo. Furthermore, we uncovered the conserved common transcriptional gene regulatory networks between in vitro and in vivo cellular liver systems that responded to TNT exposure, which mainly contain 2 subnetwork modules: PTTG1 and PIR centered networks. Interestingly, all 7 genes in the PTTG1 module were involved in cell cycle and downregulated by TNT both in vitro and in vivo.

CONCLUSIONS

The results of our investigation of TNT effects on gene expression in liver suggest that gene regulatory networks obtained from an in vitro system can predict in vivo function and mechanisms. Inhibiting PTTG1 and its targeted cell cycle related genes could be key mechanism for TNT induced liver toxicity.